Journal of the Laser and Health Academy

Vol. 2008; No.3/1; www.laserandhealth.com

State of the Art in Lasers for Dentistry

Prof. dr. Norbert GutknechtAachen Research Institute for Lasers in Dentistry (AALZ), Clinic of Conservative Dentistry,Periodontology and Preventive Dentistry, University Hospital of the RWTH, Aachen, Germany

ABSTRACT:Lasers have been used in dentistry since 1964. The ideawas to be able to treat both soft tissues and hardtissues, including bone, without direct contact,vibrations and pain. Since the early 90s lasers havebeen applied in a wide variety of dental applicationareas. In this paper Prof. dr. Norbert Gutknecht,President of the German Society for Laser Dentistry(DGL), provides an overview, discusses laserapplications and presents possible uses of lasers invarious dental application areas.

lower than with Nd:YAG lasers. 980nm diode lasers

may also be an option although high transmission isachieved due to its higher absorption in water. Thisexplains why this laser source, especially at a depth of1.000m, can only achieve 30% to 40% germreduction.

Key words: dental lasers, Er:YAG, Nd:YAG, diode,

CO2, periodontology, endodontics, implantology, periimplantitis, soft tissue surgeryINTRODUCTIONEach laser can be distinguished by its own, specificcharacteristics. The most important and principlecharacteristic is wavelength, which defines the positionof the laser in the electromagnetic spectrum. Lasertissue interaction is defined by the laser energy thatenters the tissue. Here the absorption of the laserbeams energy plays an important role and is illustratedby the absorption spectrum for each laser wavelengthin the targeted tissue and/or tissue components. Apartfrom wavelength and absorption, reflection andtransmission also play a role in laser-tissue interaction.Transmission is the degree to which the lasers energyis able to penetrate into the tissue.

Fig. 1: Representation of the channel entrance of tooth 12

Fig. 2: Nd:YAG fiber inserted the root canal of tooth 24

ENDODONTICSThe use of lasers in endodontics is aimed at eradicatinggerms in the root channel, especially in the lateraldentinal tubulus (necrotic, gangrenous pulp in thecorona and root). This requires a wavelength thatshows high transmission through hydroxyapatite andwater. The absorption curves show that Nd:YAGlasers, and in particular pulsed Nd:YAG lasers, arefirst-choice for this application. Nd:YAG lasers showthe best results in transmission and germ reductionmeasurements. Even at penetration depths exceeding1.000m, 85% germ reduction is accomplished. The810nm diode laser is the second choice laser source.Micro-biological studies have shown that this sourceprovides the second highest germ reduction,approximately 63%. This is nevertheless significantly

All other wavelengths such as Er:YAG, Er,Cr:YSGG

and CO2 lasers are not applicable in endodontics.Their absorption in hydroxyapatite and water is sohigh that germ reduction would predominantly onlytake place in the main canal, although germ reductionthrough thermal effects can still be detected in thelateral dentinal tubuli up to depths of 300m to400m. These wavelengths are not very suitable forendodontic treatments. Er:YAG and Er,Cr:YSGGlasers can however be successfully used to removeorganic tissue and smearlayers.

State of the Art in Lasers for Dentistry

Fig. 3: Master point image of tooth 12

Fig. 4: Situation after root filling of tooth 12.

LASER-ASSISTED PERIODONTICS

of Nd:YAG lasers. However the interaction with soft

tissue is higher and thus the thermal effects anddamage to the surrounding tissues is morepronounced. This means that treatments with the810nm diode laser cannot be performed withoutanesthesia.

In the periodontics the closed curettage, with a probe

depth of 5mm to 6mm, and the open curettage, withprobe depths over 6mm, are differentiated.In cases where periodontal disease is present and it ispreferred to perform a closed curettage, lasers can beused for germ reduction after having completedpretreatment and concrement removal usingconventional methods. In closed curettage proceduresonly lasers with wavelengths that do not damageadjacent tissue can be used, while these lasers mustalso show good interaction with soft tissue and thegerm spectrum present in the periodontal pocket.Pulsed Nd:YAG lasers fulfill both requirements; theyeradicate germs that have accumulated on the hardtissue surface and, because Nd:YAG lasers interactwith pigmented surfaces, reduce germs in periodontalpockets extremely well. 96% of germs in periodontalpockets are pigmented and can thus be selectivelyeradicated by Nd:YAG lasers. Nd:YAG lasersinteraction with soft tissue is relatively gentle, i.e. itdoes not involve any substantial soft tissue damage orremoval. They provide a relatively conservativeprocedure and are associated with rapid woundhealing. With Nd:YAG laser procedures, anesthesia isrequired in less than 50% of cases.Alternatively 810nm diode lasers show very goodinteraction with pigmented tissues and thus also inducevery high germ reduction, which is similar to that

980nm diode lasers can also be considered for laserassisted closed curettage procedures. Their highabsorption and interaction with water in theperiodontal pockets lead to a high germ reduction.However, their lower interaction with hemoglobinincreases the thermal effect in the tissue. If this lasersource is not applied with extreme caution inperiodontic procedures, surface necroses may becaused. In addition, relatively high tissue temperaturesare reached and anesthesia is necessary.In laser-assisted open curettage procedures Er:YAGlasers are clearly and unambiguously first choice. Inspecial cases a CO2-laser (10.6m; cw=continuouswave) may be indicated. The Er:YAG laser device ofchoice for open curettage procedures is a system that,above all, should allow a wide selection of pulseduration and repetition rate settings. These featureswill allow extremely good inter-radicular andinterdental cleaning to be carried out, while bone tissuecan be very efficiently freed from infected soft tissue.Moreover, a very fine retentive pattern on the root andbone surfaces can be created, which is of greatimportance for reattachment.

Journal of the Laser and Health Academy

Vol. 2008; No.3/1; www.laserandhealth.com

If the Er:YAG laser device allows the practitioner to

vary the pulse duration during the open curettageprocedure, then short pulses from 60s to 120s arerecommended. At these settings thermal effects areextremely low and thus thermal damage is not to beexpected. Post-operative bleeding is minimal, so thatproblem-free wound healing will occur. Er,Cr:YSGGlasers also belong to the category of erbium lasers, andcan be used in open curettage procedures. However, itmust be noted that their absorption in water isexponentially two to three times lower than that ofEr:YAG lasers. Their thermal effects on the tissue aremuch higher if not administered correctly.

Fig. 5: Removal of the closed bone cover with the Er:YAG laserto present the root point.

IMPLANTOLOGYThere are several wavelength options to uncoverimplants. The first wavelength ever used to uncoverimplants was the 10.6m CO2-laser, although thattissue surface carbonization was a small disadvantage.As an alternative the 810nm and 980nm diode laserscan be used, although the thermally damaged areas arelarger than with CO2-lasers. Very good results can beachieved with Er:YAG lasers, if the laser device offersthe possibility to vary pulse duration or if specialsurgical tips can be used. With pulse duration settingsbetween 800 s and 1000s, tissue interaction leads tohigher thermal effects. This enables smaller vessels tobe sealed without leaving areas of carbonized ornecrotic tissue. While a tendency for light bleedingthrough larger vessels remains, this in fact leads tofaster wound healing, less post-operative swelling andless inflammation in the wound area, compared todiode and CO2-lasers. Considering the physiologicalaspects of wound healing, Er:YAG lasers are the idealmodality to uncover implants. Implant damage doesnot occur with CO2, Er:YAG and Er,Cr:YSGG lasersbecause their wavelengths have a high reflectionpotential and thus hardly any absorption in metallicsurfaces. Pulsed Nd:YAG lasers are unsuitable touncover implants.

Fig. 6: Resection of the root point with the Er:YAG laser.

Fig. 7: Removal of the granulated tissue with the Er:YAG

laser; subsequent germ reduction in the depth of the bone or theresection cavity performed using the Nd:YAG laser.

PERI-IMPLANTITISThe treatment of peri-implantitis is performed similarlyto closed or open curettages in periodontics. BothNd:YAG and diode lasers have their application areasin this field. Most studies on the treatment of periimplantitis are based on 810nm diode lasers.The best procedure to treat a large peri-implantitisdefect is however uncovering the implant that hasbeen affected by inflammation. Only under suchvisibility conditions is it possible to completely removethe granulation tissue and infected tissue.

Fig. 8: Situation immediately after completion of the root point

resection..

State of the Art in Lasers for Dentistry

More importantly, this is the only way that infected

tissue in the implants contortions can be reached.Short pulsed Er:YAG lasers are the ideal modality. Theshorter the pulses, the more efficiently the granulationtissue can be removed to clean the implant surfacewithout problems. With pulse durations between 60sand 200s and very low energy settings, the infectedtissue can be cleared away very efficiently. Similar goodresults have also been achieved with Er,Cr:YSGGlasers.SOFT TISSUE SURGERYFor soft tissue cutting, e.g. abscess incisions, where asterile cut with as little bleeding as possible is required,both the 810nm and 980nm diode lasers, as well as thepulsed Nd:YAG laser can be used.Surgical procedures in soft tissue require a cautiousapproach. 810nm diode and CO2 lasers are very wellsuited for frenectomies (operations on the frenula ofthe lips, cheeks or tongue). Caution is required whenusing Nd:YAG and 980 nm diode lasers because thehigher thermal effect of these wavelengths (< 100s)can very often cause necroses.Er:YAG laser systems that allow very long pulseduration settings (> 700s) are also suitable forfrenectomies and soft tissue surgical procedures ingeneral. Er,Cr:YSGG laser and basic Er:YAG lasersystems can also be used in soft tissue surgery, butonly with special surgical tips.The difference between CO2 and long pulse Er:YAGlasers lies in their differing absorption coefficients.Er:YAG lasers are much more strongly absorbed inthe water; i.e. the soft tissue is already isolated throughthe lasers interaction with water in the cells, withoutrequiring any high thermal effect. Micro-rupturesoccur and with this bleeding follows. CO2 lasers on theother hand, show very high absorption on the tissuesurface. Due to these lasers different mode ofoperation mostly continuous wave operation thethermal effects are more pronounced on the uppertissue layers and less in the deeper tissue layers thanwith Er:YAG lasers. This leaves a carbonized uppertissue layer although bleeding is less pronounced. Withvery long pulse durations, long pulse Er:YAG lasersystems can provide a very good alternative, as thethermal effect is higher and thus smaller vessels aresealed. Bleeding is thus reduced but not completelyeliminated, which in turn leads to faster healing.

depth. Penetration depth should always be looked at in

connection with the respective wavelength and the tobe-treated tissue. In general, penetration depth is keptto a minimum by tuning the wavelength to the targettissue. There is only one meaningful exception wheretransmission is desired, and that is when treatinginfected hard tissue in the root canal or infected bonematerial. In this case germ reduction in the deeperlayers is required. In all other cases absorption of thelaser light in the tissue should be as high as possible.The higher the penetration depth, the less the thermaleffects in deeper tissue layers can be controlled and thehigher the risk for necroses.The wide-spread and repeatedly-voiced belief thatNd:YAG lasers have the highest penetration depths inthe soft tissue is only partly correct. It is correct thatNd:YAG lasers would have an extremely highpenetration depth, if we were to use a regular industriallaser, with continuous wave mode of operation andnon-contact laser power delivery. The Nd:YAG lasersystems that have been introduced into dentistry byvarious manufacturers are free-running pulse Nd:YAGlasers. Their pulse durations lie between 90s and150s, their laser energy is delivered through a fiberonto the target tissue or through direct contactbetween the fiber and the tissue. Penetration depth isthus significantly reduced. Professor Dr. Joel Whitefrom the University of California, San Francisco(UCSF) conducted a very descriptive study thatsupports this. A study conducted at the RWTH,Aachen, proves that a free-running pulse Nd:YAGlaser has a penetration depth of approximately 0.1mmto 0.3mm, whereas a continuous wave mode Nd:YAGlaser has a penetration depth of up to 6mm.

DISCUSSION

For diode lasers repetition rate and pulse duration are

specific to their application areas. From a fundamentaltechnical-physical viewpoint diode lasers deliver acontinuous laser beam and are thus continuous wavelasers. If the diode laser system is capable of deliveringthe laser in pulses, i.e. an interrupted laser beam, it is apulsed diode lasers. Pulsing is achieved byelectronically switching the laser on and off. It must beunderstood that with this method the laser power in apulse is not increased, and is in the order of severalWatts. On the other hand, free-running pulse Nd:YAGlaser systems can generate high peak powers whereindividual pulse powers can reach several thousands ofWatts. This allows this type of lasers to deliver therequired energy to the target tissue before theabsorbed heat can dissipate from the treated area.Free-running Nd:YAG lasers are therefore for thesame intended effect less damaging to the untreatedsurrounding tissue.

Laser penetration depth is of paramount importance,

especially in the medicine and dentistry. But it wouldbe wrong to base an evaluation solely on penetration

Although no comparative studies have been conducted

to investigate the need for water-spray cooling in diodelaser procedures, from a biophysical point of view it

Since 1992, Prof. Dr. Norbert Gutknecht has been the

head of the Aachen Research Institute for Lasers inDentistry (AALZ) at the Clinic of ConservativeDentistry, Periodontology and Preventive Dentistry atthe University Hospital of the RWTH in Aachen,Germany. He is co-founder and president of theGerman Society for Laser Dentistry (DGL) andOrganizing Chairman of the International Society forLasers in Dentistry - ISLD. As Editor of the Laser inMedical Science Journal and as a visiting Professor atthe University of Nice and Sao Paulo, he is anestablished expert in Laser Dentistry. His national andinternational workshops on indications and treatmentexpectations in laser-based dental therapy are widelyvisited.REFERENCES1. Proceedings of the 1st International Workshop ofEvidence Based Dentistry on Lasers in Dentistry,Quintessence Publishing, 2007, ISBN 978-1-85097167-22. Dental Magazin, 3/2006 and 4/2006, Tendenzen:Laseranwendungen in der Zahnheilkunde.